1. Field of the Invention
The present invention generally relates to a coilless AC/DC power supply device, and more particularly, to an AC/DC power supply device, in which the AC voltage is converted into the desired DC voltage by rectification and voltage leveling process. In the present invention, a transformer is not necessary during voltage leveling process. Therefore, complicated winding fabrication is omitted which leads to a reduced fabrication cost. On the other hand, such an AC/DC power supply device is downsized and can be integrated with other application circuits.
2. Description of the Prior Art
Due to the downsizing trend as well as the fast developing techniques of modern electronic products, feasibility of realization of compact electronic products is made possible. For most of the conventional electronic products, the power required is provided by converting the AC voltage into the desired DC voltage. On the other hand, in larger scale IC applications, matching condition of the supplied power must be also taken into consideration. However, most of the modern electronic products are provided with power by the conventional AC/DC power supply device composed of a transformer and a rectifier circuit. Please refer to FIG. 1, which is a schematic circuit diagram illustrating a conventional AC/DC power supply device in the prior art. As shown in the drawing, an AC voltage is input into the transformer T1 where the AC voltage is transformed and then delivered to a node a. Then, a bridge full-wave rectifier compose of a diodes D1, D2, D3 and D4 performs full-wave rectification upon the AC voltage and the AC voltage is converted into a DC voltage delivered to a node b. The DC voltage charges a capacitor C1 and then outputs a DC voltage VDC across a load resistor RL. Therefore, the voltage conversion is accomplished.
However, the above mentioned conventional AC/DC power supply device requires two complicated coils, electrically insulated from each other but wound on the same core to construct a transformer T1. Therefore, the size of such an AC/DC power supply device is limited and mismatches the downsizing trend of modem ID techniques.
It is therefore a main object of the present invention to provide a coilless AC/DC power supply device, which controls the voltage level of the required power using a voltage detecting device and a matching rectifier circuit so as to provide a reliable power source without needing a transformer composed of coils.
It is another object of the present invention to provide a coilless AC/DC power supply device, wherein the coilless design not only downsize the AC/DC power supply device but also make it possible to be integrated with other application circuits.